Assessing Sensory and Motor Fusion

Question 1

Prism moves images to the _________ and light to the _________

Answer 1

apex, base

Question 2

What is the process by which the stimuli individually sensed by each eye is combined to form a synthesized single percept?

Answer 2

sensory fusion

occurs in the brain; the ability to “see” single; despite having 2 eyes with different views of the world

Question 3

Which type of fusion consists of relative movements of the eys to achieve simultaneous retinal stimulation of corresponding retinal areas?

Answer 3

motor fusion

the movements of the eye that allow sensory fusion to occur

Question 4

What is 1st degree sensory fusion?

Answer 4

superimposition of two distinct images

Question 5

What is 2nd degree sensory fusion?

Answer 5

Fusion of 2D images; “flat fusion”

Question 6

What is 3rd degree sensory fusion?

Answer 6

stereovision

Question 7

What is the inability to perceive normally visibly objects in all or part of visual field?

Answer 7

suppression

often around fovea/macula with periphery intact

Question 8

What is the cause of suppression?

Answer 8

active cortical inhibition

Question 9

Why does suppression occur?

Answer 9

in order to preserve semblance of binocularity

Question 10

What are the two theories of the development of suppression?

Answer 10

1. classical model
2. Pratt-Johnson

Question 11

Under the classical model of suppression, how many areas must be suppressed?

Answer 11

two areas must be suppressed

fovea: elimination of confusion; peripheral retinal point: elimination of diplopia

Question 12

Where is the zone of suppression under the classical model of suppression?

Answer 12

From F to Z

Question 13

Under the Pratt-Johnson theory of Suppression, where does suppression occur in patients with strabismus?

Answer 13

strabismic patients without fusion suppress area of overlap in deviated eye

assumes a binocular field of vision

Question 14

Hemi-retinal trigger in ET

Answer 14

trigger of a temporal point (by prism, or surgery), leads to diplopia while trigger of a nasal point will lead to suppression

XT is opposite

Question 15

when is suppression bilateral?

Answer 15

alternating strabismus

Question 16

when is suppression intermittent?

Answer 16

intermittent strabismus

Question 17

what does the depth of suppression indicate?

Answer 17

the ease with which suppression can be broken

correlated with the frequency of deviation, NOT the magnitude

Question 18

What type of viewing conditions does shallow suppression occur?

Answer 18

only present under most natural viewing conditions

Question 19

What type of viewing conditions does deep suppression occur under?

Answer 19

most viewing conditions, natural or otherwise

Question 20

What are sensory and motor fusion tests done during a comprehensive exam?

Answer 20

sensory: stereo
Motor: NPC, vergence ranges

(RDS is highest level of sensory fusion)

Question 21

What instrument is used for in-instrument evaluation of sensory and motor fusion?

Answer 21

major amblyoscope

Question 22

What are the 4 possibilities for sensory fusion?

Answer 22

• sensory fusion
• unstable fusion w/o suppression
• unstable fusion w/ suppression
• suppression

Question 23

How to we assess correspondence when a patient has stable fusion?

Answer 23

UCT

If NC, then assess motor fusion via vergences with prism bar or phoropter

Question 24

What are 2 reasons for unstable fusion?

Answer 24

1. deficient motor ability to align images
2. Deficient sensory ability to combine stimuli into single percept

Question 24

How do we differentiate between unstable fusion due to poor motor ability and unstable fusion due to poor sensory ability?

Answer 24

Decrease the motor demand by introducing prism

Question 25

what should always be evaluation regardness of strabismus or sensory/motor fusion status?

Answer 25

stereopsis evaluation ## Footnote novel stimulus of 3D images can prompt alignment of the eyes even when there is poor alignment with 2D images

Question 25

What do you do if fusion is still absent or unstable after reducing motor demand?

Answer 25

try in instrument evaluation

Question 26

what movement do we record when performing in-instrument evaluation?

Answer 26

net movement

Question 27

What is the problem with lateral disparity tests?

Answer 27

monocular cues ## Footnote contaminates results

Question 28

constant strabs in the cotter study were unable to see which targets?

Answer 28

random dot e ## Footnote if a patient can see random dot targets, they can not be a constant strab

Question 29

can a patient with anomalous correspondence see random dot stereograms?

Answer 29

no ## Footnote implication: if a patient has RDS acuity, then we know they have normal correspondence

Question 30

how is anomalous motor fusion assessed?

Answer 30

prism adaptation test

Question 31

in the prism adaptation test, what power is the prism used for the 2nd PACT?

Answer 31

the original neutralizing prism ## Footnote performed after patient wears the prism for 30-45 minutes

Question 32

how do we measure the strength of anomalous motor fusion?

Answer 32

progressive prism adaptation test ## Footnote keep adding prism until the patient stops adapting